Compression plate for osteosynthesis

ABSTRACT

A compression plate for the retention and internal fixation of fragments resulting from a bone fracture. The compression plate is of generally elongate structure and is adapted to be attached to both pieces of the broken bone by screws fitting within slots generally aligned with the length of the compression plate. At least one of the slots in the compression plate is formed with a slot having a taper, generally defined by a portion of the arc of a first hole through the compression plate, a portion of the arc of a second hole through the compression plate, larger in diameter than the first hole and closer to the end of the plate, and lines which are tangential to both holes. The top surface of the tapered slot is preferably chamfered so as to better mate with a screw having a tapered head. Thus, tightening of the screw in the tapered hole causes progression of the compression plate along its axis to encourage and retain the fracture surfaces in firm abutment.

United States Patent [191 Kondo Dec. 18, 1973 1 COMPRESSION PLATE FOROSTEOSYNTHESIS [76] Inventor: Shigeru Kondo, 13 Kamibanba-cho,

.lodoji, Kyoto, Sakyo-ku, Japan [22] Filed: Mar. 3], 1972 [21] Appl.No.: 240,243

[52] US. Cl 128/92 D [51] Int. Cl. A6lf 5/04, A6lb 17/18 [58] Field orSearch 128/92 D, 92 R [56] References Cited FOREIGN PATENTS ORAPPLICATIONS 1,505,513 11/1967 France 128/92 D 462,375 10/1968Switzerland 128/92 D Primary Examiner-Richard A. Gaudet AssistantExaminer-Ronald L. Frink [57] ABSTRACT A compression plate for theretention and internal fixation of fragments resulting from a bonefracture. The compression plate is of generally elongate structure andis adapted to be attached to both pieces of the broken bone by screwsfitting within slots generally aligned with the length of thecompression plate. At least one of the slots in the compression plate isformed with a slot having a taper, generally defined by a portion of thearc of a first hole through the compression plate, a portion of the arcof a second hole through the compression plate, larger in diameter thanthe first hole and closer to the end of the plate, and lines which aretangential to both holes. The top sur face of the tapered slot ispreferably chamfered so as to better mate with a screw having a taperedhead. Thus, tightening of the screw in the tapered hole causesprogression of the compression plate along its axis to encourage andretain the fracture surfaces in firm abutment.

4 Claims, 10 Drawing Figures COMPRESSION PLATE FOR OSTEOSYNTI-IESISBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to the field of surgical devices for use inosteosynthesis.

2. Prior Art In certain instances broken bone fragments must bemechanically retained one to the other if they are to properly knit.Thus, in cases involving such injuries, an operation is generallyperformed to expose the bone fragments and to fasten a steel plate tothe fragments in a suitable manner to retain the fragments as required.

In the prior art, various devices are known for urging the bonefragments into their proper orientation and to retain them as desired.Typically such devices comprise two major components, the first beingthe plate which will be permanently attached to the bone, and the secondbeing a means for urging the bone fragments into their properorientation and which will be removed once the fragments are properlyorientated and retained one to the other. By way of example, one suchprior art device uses a steel plate having a pair of screw holesadjacent to each end so that two screws may be applied therethrough intothe bone fragments to retain the fragments as desired. In use the plateis attached by two screws to one of the bone fragments so as tooriginally attach the plate thereto. A third screw is attached to theremaining bone fragment, generally remote to the final position of theplate with respect to that fragment, and is used to secure a screw clampdevice to that bone fragment. The screw clamp device is adapted toextend from the third screw to one of the remaining pair of screw holesin the plate, so that by manipulation of the screw plate device, theplate and thus the bone fragment attached thereto may be urged intoproper knitting position with respect to the second bone fragment. Oncein place, a fourth screw is attached to the adjacent bone fragmentthrough the heretofore unused screw hole in the plate and finally thescrew clamp device and screw used to retain the device are removed andanother screw is attached to the bone fragment through the remaininghole in the plate.

It is to be noted that in the above apparatus, more bone must be exposedthan is required to receive the steel plate, a screw must be insertedinto the bone which is not used for retaining the plate, but is merelyused to provide a bone connection against which the screw clamp devicemay pull the bone fragments into place, and the apparatus itself tendsto be large and clumsy in attachment and use.

BRIEF SUMMARY OF THE INVENTION A compression plate for the retention andinternal fixation of fragments resulting from a bone fracture. Thecompression plate is of generally elongate structure and is adapted tobe attached to both pieces of the broken bone by screws fitting withinslots generally aligned with the length of the compression plate. Atleast one of the slots in the compression plate is formed with a slothaving a taper, generally defined by a portion of the arc of a firsthole through the compression plate, a portion of the arc of a secondhole through the compression plate, larger in diameter than the firsthole and closer to the end of the plate, and lines which are tangentialto both holes. The top surface of the tapered slot is preferablychamfered so as to better mate with a screw having a tapered head. Thus,tightening of the screw in the tapered hole causes progression of thecompression plate along its axis to encourage and retain the fracturesurfaces in firm abutment.

Preferably one tapered hole is used at each end of the compressionplate, together with a slot at each end of the compression plate toreceive a second retaining screw when compression has been accomplished.Substantial compression forces and range of compression may be achievedthrough the tightening of the screws in the tapered holes at each end ofthe compression plate, since rotation of the screw tends to eliminatestatic friction between the screw and the compression plate, therebyaiding in the progression of the compression plate as the screws aretightened.

BRIEF SUMMARY OF THE DRAWINGS FIG. 1 of the perspective view of oneembodiment of the present invention compression plate.

FIG. 2 is a top view of a portion of the compression plate of FIG. 1.

FIG. 3 is a side view of the tapered screw used with the compressionplate of the present invention.

FIG. 4 is a cross-section taken along lines 4 of FIG. 1.

FIG. 5 is a top view of a section of the preferred embodimentcompression plate showing the sliding hole therein.

FIG. 6 is a cross-section taken along line 6-6 of FIG. 5.

FIG. 7 is a cross-section taken along line 77 of FIG. 5.

FIG. 8 is a cross-section of FIG. 7 showing the screw at a further stageof insertion.

FIG. 9 is a cross-section taken along lines 99 of FIG. 5 after the screwhas been tightened in the sliding hole so as to progress to a widerposition of the pear shaped hole to effect compression.

FIG. 10 is a cross-section similar to FIG. 8 illustrating the possiblemisalignment of the screw with respect to the compression plate.

DETAILED DESCRIPTION OF THE INVENTION The present invention compressionplate has at least one special hole to make compression between thefragments of broken bone by sliding the plate along the bone as a resultof tightening of a screw therein. The hole is pear shaped binding alarge circle and a small circle with tangent lines. The diameter of thesmall circle is substantially the same as the overall width of the screwthreads, and the diameter of the large circle is designed to be slightlysmaller than the diameter of the screw head. The compression plate isused with a screw having a tapered head so that when the screw isinserted vertically at the center of the small circle and tightened, thetapered slope of the screw head presses against the edges of the pearshaped hole. As a result, the screw tends to move toward the center ofthe large hole, namely toward the middle of the plate, and as a resultthe plate is forced to move with respect to the screw along the boneshaft, creating the desired compression over the fractured surfaces. Thescrew, of course, remains both to retain the desired compression and tofurther aid in retention of the compression plate. In the preferredembodiment, one such pear shaped hole is used adjacent each end of thecompression plate with an additional slot of ordinary configurationadjacent thereto, so that two additional screws may be inserted tobetter retain the bone and compression plate in the desired position.

Thus, the various aspects of one embodiment of the present invention maybe seen in FIGS. 1 through 4. In the following, the surgical techniquewith the present invention plate is instructed. Numeral 21 refers to theinternal plate with both edges thickened (22 and 22a) so that a grooveis made between 22 and 22a; this groove being identified as 23.

In FIG. 2, the sliding hole is instructed. In this figure a refers tothe large circle and the small circle is referred to as b, while 24identifies the hole itself. The tangential lines binding a and b areidentified as c which are filed (chamfered) slightly. In FIG. 3, 25 isthe screw head, 25:: is thehead outer diameter and 25b is the underside,having tapered slope. The angle of the taper is indicated as p, theincluded angle of which preferably is 60 to 70 to make the sliding between 25b and c smoother. (This screw is hereafter referred to assliding screw).

After the sliding screw is fully inserted and tightened up to makecompression ove the fracture surfaces, an ordinary screw is insertedinto ordinary hole (27 and 27a) to affix the plate tightly. Theseordinary holes are referred to as fixation holes.

In FIGS. 1 and 4, the bone fragment are named as 28 and 28a and thefracture surfaces are also named as 28b and 28c. Using the presentinvention, the tapered slope 25b of the sliding screw 25 and the slidinghole 24 make compression over the fracture surfaces 28b and 280 to closethe spaceQThe surgical technique is easy and very simplified whencompared with prior art compression plates.

Now referring to FIGS. 5 through the preferred embodiment of the presentinvention may be seen. This embodiment is very similar in organization,though the plate is considerably thicker to better cooperate with thesliding screws, and the thickened edges have been eliminated. In thisimproved embodiment, contact of the screw with the compression platewhich results in the desired compression is much smoother and thesliding becomes better. Furthermore, the stability of the screw isimproved in this embodiment. In these figures (FIGS. 5 through 10) thecompression plate is named as 41 and the sliding hole is 42. As before,the large circle of the sliding hole is (1", while the small circle isb. A screw to insert into the sliding hole is 43 and the bone fragmentis 44.

From FIGS. 5 to 10, it may be seen that the external edge of the hole is45 and the slope surrounding the hole is 46. This slope fits the taperslope of a screw and internal edge of the slope 47. The slope 50 is thesame inclination as slope 46 and as before is preferably in the range of60 to 70. In FIGS. 6 and 10, the screw head is 48 and the taper slope is49; this angle coincides the inclination of 46 and 50. The screw shaftwith threads is 51.

From these conditions, there are several merits in the improved slidinghole, when compared with the prior art. They are as follows:

a. An ordinary screw can be used for the sliding screw so long as thetaper slope and the slope of the hole edge coincide. A special screw isnot necessary in the new hole. (FIG. 6 through 9).

b. As the taper slope of the screw and the inclination of the hole edgecoincide, the screw is more stable than the former one (FIG. 9).

e. The screw can be stable even though the screw head 48 is insertedbeneath the plate surface (FIG. 9). Accordingly, danger of compressionby the screw head against the soft tissue, including the skin, can beavoided. Some parts, where the soft tissues are thin, there is apossibility of necrosis of the skin when compressed by the screw head,(for example, the medial aspect of the lower leg, ulnar side of theforearm, etc., (FIG. 9).

d. It is preferable that the screw be inserted vertically, but in thepreferred embodiment sliding hole, some error can be neglected, becausethe deeper the screw head is inserted, the wider the hole becomes. Thesliding can be made even if the screw is inserted a little obliquely, asin FIG. 10.

Thus, it may be seen that by use of the present invention, only theportion of the bone on which the compression plate will be placed needbe exposed as a result of an incision, and no screws are required to beap plied to the bone other than screws used to retain the compressionplate. Substantial compression force as well as range of motion of thecompression plate are achieved, and once the compression plate isgenerally placed in the desired position, compression is quickly andsimply accomplished by merely tightening of the screws retaining theplate in the proper sequence, that is, first tightening the screws inthe pear shaped holes so as to achieve the desired compression, and thentightening of the remaining holes to accomplish the final retention ofthe compression plate.

I claim:

I. A compression plate having a top surface, a bottom surface and atleast one pear shaped slot therethrough, said slot being generallycharacterized by a first opening at one end of said slot and a secondopening at the second end of said slot, said second opening beinggreater in width than said first opening, said slot having a horizontalwidening starting at said first opening and joining said first andsecond openings, said slot being bound by a side wall of uniform contourfrom said one end to said second end thereby defining a pear shapedopening at said top surface which extends continously downwardly throughthe plate to terminate in a pear shaped opening at said bottom surface.

2. The compression plate of claim 1 wherein said pear shaped slot has achamfered area adjacent its upper edges.

3. A compression plate having a top surface, a bottom surface and atleast one pear shaped hole therethrough, said hole being generallydefined by the horizontal widening of a slot binding with tangent linesa small circle on one end of said slot and a large circle at the otherend of said slot, said slot being bound by a side wall of uniformcontour from said one end to said other end thereby defining a pearshaped opening at said top surface which extends continously downwardlythrough the plate to terminate in a pear shaped opening at said bottomsurface.

4. The compression plate of claim 3 wherein said pear shaped hole has achamfered area adjacent its upper edges.

1. A compression plate having a top surface, a bottom surface and atleast one pear shaped slot therethrough, said slot being generallycharacterized by a first opening at one end of said slot and a secondopening at the second end of said slot, said second opening beinggreater in width than said first opening, said slot having a horizontalwidening starting at said first opening and joining said first andsecond openings, said slot being bound by a side wall of uniform contourfrom said one end to said second end thereby defining a pear shapedopening at said top surface which extends continously downwardly throughthe plate to terminate in a pear shaped opening at said bottom surface.2. The compression plate of claim 1 wherein said pear shaped slot has achamfered area adjacent its upper edges.
 3. A compression plate having atop surface, a bottom surface and at least one pear shaped holetherethrough, said hole being generally defined by the horizontalwidening of a slot binding with tangent lines a small circle on one endof said slot and a large circle at the other end of said slot, said slotbeing bound by a side wall of uniform contour from said one end to saidother end thereby defining a pear shaped opening at said top surfacewhich extends continously downwardly through the plate to terminate in apear shaped opening at said bottom surface.
 4. The compression plate ofclaim 3 wherein said pear shaped hole has a chamfered area adjacent itsupper edges.